What knock is
Knock, or detonation, happens when part of the air-fuel mixture ignites on its own after the spark, instead of burning smoothly. The pressure spike rings through the block like a hammer tap. A little is a warning sign; a lot can break pistons and ring lands quickly, especially on boosted engines.
How the ECU detects and controls it
A knock sensor bolted to the block picks up vibration. The ECU filters that signal to the frequency range where knock shows up and listens only during the window when each cylinder could be knocking. If the level crosses a threshold, it retards ignition timing, then gradually adds it back once the knock stops.
Getting that threshold right is the whole job. Set it too sensitive and the ECU pulls timing for normal engine noise. Too dull and real knock slips through. That's why we set up knock control with proper listening equipment on the dyno.
Where to go next
Our knock control user's guide goes step by step, and what is knock and why you should control it covers the theory. Want help setting it up? Book a free consultation.
